The present studies were aimed to determine the effects of iron and manganese on nutritional physiology in juvenile gibel carp(Carassius auratus gibelio) and to evaluate the hematological effects of gossypol on southern catfish（Silurus meridionalis）and common carp（Cyprinus carpio Linnaeus）. The gibel carp study consisted of two growth trails. In the first trail, a 83-day growth trail was conducted using a flow-through system to determin the dietary iron requirement of juvenile gibel carp (Carassius auratus gibelio). Six purified diets supplemented with different levels of iron (0, 10, 30, 60, 100 and 200 mg/kg) (as ferrous sulfate) were fed to triplicate groups of fish (initial weight 2.12±0.00 g per fish). In the second trail, a 68-day growth trial was conducted in a flow-through system to determine the dietary manganese requirement of juvenile gibel carp (Carassius auratus gibelio). Seven purified diets containing 7.21, 8.46, 9.50, 10.50, 13.03, 19.72 and 22.17 mg manganese (as manganic sulfate) per kilogram diet were fed to triplicate groups of fish (initial weight 3.21±0.01 g). The gossypol study consisted of two acute trails. In the first trail, hematological responses of southern catfish (Silurus meridionalis) to intraperitoneal injection of free gossypol were studied in a flow-through system. In the second trail, hematological responses of common carp (Cyprinus carpio Linnaeus) to intraperitoneal injection of free gossypol were studied in a flow-through system.
The main results were shown as follows:
1. The addition of iron to the basal diet did not significantly affect the specific growth rate (SGR), feed efficiency (FE), survival, red blood cell amount (RBC), hemoglobin content (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC). Hepatic iron concentration and hematocrit (Hct) were significantly influenced by dietary iron level (P<0.05). On the basis of the iron concentration for the maintenance of optimum hepatic iron concentration and Hct, the dietary iron requirement of juvenile gibel carp was estimated to be approximately 202 mg Fe/kg diet.
2. Dietary manganese levels did not significantly affect feed intake of the fish. Specific growth rate, feed efficiency, total hepatic superoxide dismutase activity, carcass and skeletal manganese concentrations increased significantly with increased dietary manganese (P<0.05) while condition factor decreased significantly (P<0.05). Dietary requirement of manganese was 13.77 mg Mn per kilogram diet.
3. The 24-h, 48-h, 72-h, 96-h LC50s for southern catfish to free gossypol were 225.21 mg/kg, 84.62 mg/kg, 59.91 mg/kg, 55.68 mg/kg, respectively. This is the first to determine LC50s of gossypol to aquatic animals. In a sub-lethal test, changes in red blood cell count (RBC), hemoglobin content (Hb) and hematocrit (Hct) of the catfish were measured after 24-, 48-, 72- and 96-h of exposure to 0, 20 and 40 mg gossypol/kg BD. Compared with the control, fish in the high-dose group showed a time-dependent decrease in RBC, Hb and Ht (P<0.05), with statistically significant alterations at 48 h post injection, while fish in the low dose group did not show significant difference in RBC count, Hb and Ht (P>0.05). Compared with the control, fish in the high-dose group showed abnormal erythrocyte features and hemolysis. One possible mechanism of anemia caused by free gossypol might be hemolysis.
4. The 24-h, 48-h, 72-h, 96-h LC50s for common carp to free gossypol were 236.80 mg/kg, 118.27 mg/kg, 80.96 mg/kg, 71.11 mg/kg, respectively. In a sub-lethal test, red blood cell count (RBC), hemoglobin content (Hb) and hematocrit (Hct) of the catfish were measured after 24-, 48-, 72- and 96-h of exposure to 0, 20 and 60 mg gossypol/kg BD. Compared with the control, fish in the high-dose group showed a time-dependent decrease in RBC, Hb and Ht (P<0.05), with statistically significant alterations at 48 h post injection, while fish in the low dose group did not show significant difference in RBC count, Hb and Ht (P>0.05). Compared with the control, fish in the high-dose group showed siganificantly higher maximal and mimimal fragility than fish in other treated groups. Similar to southern catfish, one possible mechanism of anemia in common carp caused by free gossypol might also be hemolysis.